Our objective is to understand the role that glycoproteins paly in membranes of eucaryotes. Since the carbohydrate moiety of glycoproteins is involved in a variety of recognition phenomena between cells and their environment the aim is to understand the mechanisms which determine the specific carbohydrate structures expressed on glycoproteins. We therefore plan to investigate some aspects of glycoprotein biosynthesis in Saccharomyces cerevisiae. It is known that the inner core of the mannoproteins in this organims is synthesized in a manner analogous to the formation of N-linked oligosaccharides in glycoproteins of higher organisms, i.e., through the transfer of a preformed oligosaccharide precursor containging clucose, mnnose and N-acetyl-glucosamine from dolichly pyrpophosphate to protein acceptor. Following this transfer, processing of the oligosaccharide begins with the removal of the glucose and some of the mannose residues. The final structure of the carbohydrate moiety is therefore dependent upon these initial stages involving the action of glycosidases. We plan to study the glucosidases and mannosidase(s) involved in processing in Saccharomyces cerevisiae. The glucosidases form this organism are obtained in a stable soluble form without using detergent, a property which makes them more amenable to purification than the corresponding enzymes from animal cells. A purification scheme for these enzymes will therefore be developed, and their specificity with respect to structure of the oligosaccharide moiety and to the amino acid sequence near the site of glycosylation will be investigated using synthetic peptides. These studies should help to identify specific inhibitors of processing, and to elucidate the role of glucose residues in the oligosaccharide precursor.